Threaded pipe construction



y 1968 v. F. MICHAEL 3,381,716

THREADED PIPE CONSTRUCTION Original Filed Oct. 12, 1962 2 Sheets-Sheet 1 Media 'WE' g Wm, 73:1 am 'Mfd/W;

May 7, 1968 v. F. MICHAEL 3,331,716

THREADED PI PE CONSTRUCT ION Original Filed Oct. 12, 1962 2 Sheets-Sheet 2 V QVENTOR f g/M0, 95mm 5% ea/wm/ 4 1 United States Patent'() 3,381,716 THREADED PIPE CONSTRUC'IEON Vesta F. Michael, Wichita, Kans., assignor to Rock Island Oil & Refining Co., Inc., Wichita, Kans., a corporation of Kansas Original application Oct. 12, 1962, Ser. No. 230,093 now Patent No. 3,291,881, dated Dec. 13, 1966. Divided and this application June 2, 1966, Ser. No. 554,719 6 Claims. (Cl. 138-109) 1 ABSTRACT OF THE DISCLOSURE A glass-reinforced plastic pipe is provided having pretensioned, filamentous reinforcements embedded in a cured resin. The opposed pipe ends have male and female threads formed thereon. The threads formed thereon are disposed adjacent and bonded to longitudinal glass filaments under tension whereby the shear strength of such threads is improved. Also, the female threads have helical filamentous glass reinforcements disposed in the thread crest portions to increase the hoop strength thereof.

This invention relates to glass-reinforced resin pipe, and this application is a division of my copending application Ser. No. 230,093 which was filed in the US. Patent Office on Oct. 12, 1962, and now US. Patent 3,291,881. More particularly, this invention pertains to reinforced resin pipe having opposed threaded end portions comprising an internally threaded coupling end and an externally threaded male or pin end.

The use of discrete coupling members for joining the threaded adjacent ends of resin or plastic pipe is well known. However, the use of discrete coupling members has certain disadvantages. The chances for leaks are twofold since two threaded ends are joined by an interposed connector. The time and effort necessary for assembly is appreciable since each and every pipe segment must be threadedly engaged with a coupling. The opposed coupling shoulders have a tendency to catch upon sharp edges and projections if a pipe string is run into wells or other elongate openings. The latter disadvantage may be most serious in sandy formations.

In addition to the above disadvantages of use, there are certain disadvantages of manufacture encountered when resin pipe couplings are made. In the normal course of coupling manufacture the interior of the coupling shell is first roughened by a rasp or other equivalent means to permit better bonding to the threads which will be molded thereon. However, difiiculty is oftentimes experienced in obtaining desired bonding of the threads to the coupling interior because of the small interval available for concentric alignment of the mold relative to the surrounding coupling shell with resulting thread weakness. If a coupling end could be formed integrally with each resin pipe section, many disadvantages peculiar to a discrete coupling would be eliminated.

It is an object of this invention, therefore, to provide a glass-reinforced resin pipe having opposed threaded end portions, including a coupling end, which provide joints having tensile strengths fifty percent greater than joints employing similar threaded pipe used in conjunction with discrete coupling members.

It is another object of the invention to provide a novel method for forming a coupling end on a resin pipe which assures the elimination of any entrapped air in the threads formed therein, thereby providing maximum thread strength.

It is another object of this invention to provide apparatus and a novel method for forming external or male I 3,381,716 Patented May 7, 1968 threads on the pin end of a resin pipe which assures the absence of entrapped air in the resin forming the threads, as well as ready disengagement between the thread mold and the completed pipe.

It is yet another abject of this invention to provide a novel method for formation of a coupling end on a glassreinforced resin pipe in which the coupling end is formed concomitantly with the pipe, thereby necessitating only a minimum of processing time for the formation of the coupling end alone.

The above and other objects of this invention will become more apparent from the following detailed description when read in the light of the accompanying drawing and appended claims.

In one embodiment of this invention a threaded nipplelike member is snugly received over one end portion of a rotatable mandrel and locked in place thereon. A parting agent such as wax is coated on the mandrel, and a resin release agent is coated over the nipple threads. The prepared mandrel is then placed in a common lathe-type machine and a thickened mixture of a resin, such as epoxy resin thickened with a thixotropic agent, is applied over the nipple threads as the mandrel rotates. A few fine strands of material such as glass roving are wrapped spirally in the nipple or female form threads to release any entrapped air in the resin and assure uniform and complete filling of the threads.

A longitudinal assemblage of glass roving strands is placed under tension and positioned about the periphery of the mandrel. A single roving spiral of widely spaced convolutions is wrapped about the longitudinal strands which have first been saturated with resin to bring the saturated strands into close engagement with the mandrel surface. Alternate layers of longitudinal and helical roving are then applied in a known manner until the desired pipe dimensions are attained.

Following formation of the pipe on the rotatable mandrel, external threads are formed in the pin end or male end of the green uncured-pipe oppositely disposed to the pipe coupling end. The male threads are formed by means of a centrally apertured male mold having opposed ends encased in novel caps or jackets of flexible material, such as polyethylene plastic. The threads of the male thread mold are covered with a resin release agent and filled with a thickened resin composition. The thread-filled mold is then fitted over the pipe end oppositely disposed to the coupling end. The thickened resin of the mold bonds with the uncured resin covering of the green pipe. The novel plastic caps are formed so as to retain the thickened resin in the mold threads eliminating any possibility of air entrapment and resulting thread weakness in the finished pipe, as will hereinafter be explained in greater detail.

For a more complete understanding of this invention, reference will now be made to the drawing wherein:

FIGURE 1 is a fragmentary perspective view of a mandrel and associated apparatus elements employed in the formation of a coupling end in a reinforced resin pipe;

FIG. 2 is a fragmentary elevational view illustrating a longitudinal glass roving assemblage disposed about apparatus employed in the formation of a reinforced resin pipe in the initial stages of pipe formation;

FIG. 3 is a fragmentary sectional view illustrating a coupling end of a glass-reinforced resin pipe following formation thereof on a mandrel in assembled relationship with the coupling end thread mold;

FIG. 4 is a fragmentary sectional view, partly in elevation, illustrating the pin end of a resin pipe in the process of having male threads formed thereon by means of a novel mold construction;

FIG. 5 is a fragmentary top plan view illustrating one form of apparatus which may be employed in the formation of glass-reinforced resin pipe;

FIG. 6 is a longitudinal sectional view illustrating the mold illustrated in FIG. 4 and the opposed cap members secured to opposite end portions thereof prior to engagement with a pipe member; and

FIG. 7 is a perspective view of a modified cap for use with a male-thread mold.

Referring now more particularly to FIG. 1, a rotatable mandrel 10 is therein illustrated having radial apertures 12 formed therein. Secured to one longitudinal end of the mandrel is a nipple-like member 14 secured in fixed position on the mandrel by means of a screw 16 which engages a threaded opening in the nipple and lockingly engages an underlying surface portion of the mandrel 10 by means of the screw terminal end limit. Equivalent means preventing relative movement between the mandrel and nipple may be employed. It will be noted that the locking screw 16 is disposed adjacent the reduced mandrel portion 22 to facilitate subsequent nipple disengagement, as will hereinafter be explained in greater detail. The nipple 14 has a threaded portion 18 disposed innermost; the latter threaded portion comprises a thread mold for a coupling end of a glass-reinforced resin pipe which is to be formed about the mandrel and nipple assembly.

Also illustrated inFIGql is a prestressing ring 20 which is snugly received about the reduced terminal end portion 22 of the mandrel. In the normal course of use, prestressing ring 20 is urged into abutting relationship with shoulder 24 to define an anchor for longitudinal roving strands for purposes hereinafter explained.

The pipe to be made in accordance with the teaching of this invention is of the type disclosed in my U.S. Patent No. 3,202,650, issued Aug. 24, 1965. Such pipe comprises a glass-reinforced resin pipe in which alternate layers of longitudinal and helical glass roving are embedded in cured resin, such as epoxy resin. The resulting pipe has high tensile and burst strengths, as well as corrosion resistance and other desirable properties. The ultimate tensile load of a two and onehalf inch medium service tubing joint increased from about 30,000 pounds to about 45,000 when the integral coupling constructions of this invention were substituted for discrete coupling members.

Following assembly of the nipple 14 to one end portion of the rotatable mandrel 10 and positioning of the mandrel and nipple assembly together with the prestressing ring 20 in a common lathe-type apparatus schematically shown in FIG. 5, the exposed pipe-forming surface 26 of the mandrel is coated with a parting layer such as paraffin, in the manner disclosed in my U.S. Patent No. 3,231,442, issued Jan. 25, 1966. In the course of pipe formation, the parafiin coating placed about the surface 26 of the mandrel serves to prevent adherence between the formed plastic pipe and the external periphery of the mandrel. After the pipe is formed and the same, in combination with the mandrel, is exposed to acuring temperature, the heat applied for curing purposes expands the mandrel, forcing the wax or other parting material to enter the perforations 12. It is the mandrel expansion which also places the reinforcing roving of the pipe under tensile stresses while the resin of the pipe cures.

Following curing of the pipe the same may be slipped from engagement with the underlying mandrel at which time substantially all of the wax coating initially applied to mandrel surface 26 will lie in the hollow center of the mandrel from which it may be recovered for reuse. In FIG. 3 a mass of wax 27 is illustrated in the internal mandrel passageway following pipe formation.

At the same time that a parting parafiin layer is applied to mandrel surface 26, the threadsof the nipple 14 secured tothe mandrel are coated with a layer of resin parting agent 29 (see FIG. 3). The agent will assure ready disengagement between the nipple and the resin threads formed thereover following pipe completion. The parting agent may vary withthe plastic composition employed for formingthe overlying glass-reinforced threads.

Following application of the resin parting agent over the nipple 14, a quantity of resin and hardener therefor (together with a thickening agent if the resin-hardener mixture is too thin for application) is applied about the complete periphery of the nipple threads. The mixture is applied about the threads in sufiicient quantity so as to completely fill the same. This thickened mixture may be poured into the nipple threads as the mandrel is rotatably driven.

Epoxy resin reinforced by strands of glass roving which are in parallel and untwisted relationship has been found to comprise an excellent combination for use in the formation of pipe of the type herein described. However, this latter combination is given by way of example only and the apparatus and methods herein disclosed for the formation of threads on opposed end portions of the disclosed pipe may be applicable to other resin compositions employing other means of reinforcement, if any.

The following composition has been found to be ex tremely effective in formation of the threads molded about form 14 illustrated in FIG. 1: Epoxy resin, 100 parts; resin hardener (triethylene tetrarnine), 12 parts based on the weight of resin; silica powder (200 mesh), 30 parts per 100 parts by weight of the resin; and a thixotropic agent such as that sold under the brand name Cab-O-Sill, 2 parts per 100 parts by weight of the resin.

Following application of this thickened resinous mixture a few ends of glass roving (see strands 52 in FIG. 3), which may comprise about three to five filaments of glass, are wrapped spirally about the valleys of the threads 18 to assure the dispersion of any air whichmay have become entrapped in the thickened resinous mixture. The latter glass filaments may be approximately three feet in length and may be wrapped about the resin filled threads while the mandrel and connected parts are rotating. In addition to assisting in removing entrapped air, the filaments impart hoop strength to the threads which resists outwardly directed forces applied to the pipe portion containing the threads.

Following the above-described initial preparation of the mold for the threads to be internally formed on the coupling of the pipes, steps are carried out to buildup the pipe thickness in the manner disclosed in my U.S. Patent No. 3,202,560 and No. 3,231,442 by applying alternate layers of longitudinally arranged and spirially wound untwisted glass roving. As has been pointed out in my patents, it is desired that the glass filaments be in untwisted relationship. It is also desired that the glass filaments be arranged substantially transversely to the mandrel longitudinal axis in the spiral helices and arranged parallel to the mandrel longitudinal axis in the longitudinal assemblages. As a result, any tensile or bursting forces imparted to the pipe may be reacted to efli'ciently by the individual filaments of the glass reinforcement. Because of the untwisted relationship of the glass filaments, any force exerted thereon placing the same in tension will not result in any cutting action being exerted between adjacent filaments.

It is preferred that for strength purposes the initial glass filament layer applied to the mandrel surface, including that portion of the mandrel having the threaded form disposed thereon, comprise a longitudinal assemblage or sock of glass roving. The glass strands of the, latter assemblage being arranged parallel to the longitudinal axis of the mandrel may directly resist any tensile stresses imparted to the pipe along the length thereof. As is explained in my U.S. Patent No. 3,202,560, it is desired that all glass filaments incorporated in the pipe be bound in the surrounding resin under tension so that when the final cured pipe is put in use these tension forces may be utilized in resisting forces which may be applied to the pipe.

FIG. 2 illustrates a longitudinal assemblage of glass filaments 30 disposed about a mandrel and the female thread form 14, the threads thereof being shown in dotted lines. It Will be noted from this latter figure that opposed end portions of the assemblage 30 are locked in place by means of locking helices 32 and 34 wound about a prestressing ring 20 at a left sock end portion and reduced mandrel end portion 28 at a right sock end portion, respectively. In the course of pipe formation the filaments of the longitudinal strand assemblage 30 are placed under tension by means of a hydraulic piston or the like which acts to pull a locking ring (see ring 47 of FIG. 5) to which all of the ends of the glass filaments are secured away from an opposed locking ring (see ring 49 of FIG. 5) in a manner disclosed in my US. Patent No. 3,202,560. Following tensioning of the filaments of assemblage 30, looking helices 32 and 34 are wound about prestressing ring and mandrel portion 28, as illustrated, to firmly secure the ends of the assemblage in place. Since locking rings 47 and 49 must be detached from the mandrel and pipe following pipe formation, locking helices 32 and 34 assure maintenance of the longitudinal filaments under tension while the resin of the green pipe is subsequently cured.

Next, a spiral wrap of glass roving 36 having widely spaced helices is wound about the assemblage so as to bring the same into overlying contact with the underlying coated mandrel surface and nipple surface since looking rings 47 and 49 are of greater diameter than the mandrel portion defining surface 26. Prior to winding roving helix 36 about the longitudinal assemblage, sufiicient resin is applied to the assemblage 30 to assure complete resin saturation thereof. Alternate layers of helical and longitudinal glass roving are then applied until a pipe of proper dimensions has been formed. The number of spiral and helical layers varies with the intended use of the pipe and the number of layers shown in the drawings is given by way of illustration only.

FIG. 5 illustrates, in a schematic manner, apparatus also disclosed in my US. Patent No. 3,202,560, which may be employed for applying helical roving over the longitudinal assemblage 30. In FIG. 5 a platform 38 is reciprocally movable along the length of the adjacent rotating mandrel partially formed pipe assembly by means of rotating screw 40 which is driven by a reversible motor 42. Mounted on the platform 38 are two spools 43 of glass roving which are controlled so as not to rotate until a predetermined torque is applied thereto. Glass roving strands 44 are pulled from spools 43 and helically wound about the rotating mandrel and overlying strand assemblage 30 so as to form a layer 36. Simultaneously with the application of the glass roving 44, a resinhardener mixture is applied thereto so that the same is saturated upon being formed over the rotating mandrel. Numeral 48 identifies a resin-hardener dispenser adapted to saturate the glass roving being applied in the form of helices to the rotating mandrel.

FIG. 3 illustrates one end portion of a completed pipe formed in accordance with the steps of the above process. In FIG. 3, numeral 52 identifies the glass filaments which are employed for purposes of assuring dispersion of any air which may have been trapped. The threads of the nipple 14 are thus seen in FIG. 3 to be employed as a mold for female threads 54 formed in the completed pipe.

It will also be noted from the sectional view of FIG. 3 that adjacent the coupling end portion of the illustrated pipe is a builtup pipe portion 56 which is larger in diameter than the remaining portion of the pipe by virtue of extra windings 56a of helical glass filaments. It is intended that the built-up portion 56 comprise a portion of the pipe which is engaged by wrenches or other means employed in the course of assembling pipe portions into a line or string. Because of its enlarged size, portion 56 will have desired addition-a1 strength with which to resist rough handling imparted thereto. It will also be noted from FIG. 3 that to improve the strength of the coupling end portion of the pipe, additional spiral helices 61 may also be formed about the underlying threaded area thereby improving the hoop strength thereof.

It is preferred that the glass layers formed adjacent the male and female threads in the formation of the resin pipe be longitudinal strand assemblages. It is also preferred that the initial glass layer applied in the formation of the entire pipe be longitudinal. By intially applying a longitudinal glass strand assemblage to the mandrel, chances of a glass filament cutting through the internal peripheral surface of the final completed pipe are minimized. Cutting through or filament pull out is minimized since the tension exerted on the innermost filaments is exerted in a direction parallel to the longitudinal aXis of the pipe and not transversely thereto. Consequently, the disposition of the horizontal glass assemblage at the innermost layer reduces the chance of pull out of any filament through the interior pipe wall, and in addition tends to provide a uniform internal pipe periphery free from any protuberances, such as would more likely occur if a spiral wrap were the initial layer.

The presence of an inwardly directed protuberance on the pipe surface is objectionable when a reciprocating object is disposed in the pipe interior. A pipe may be employed in a pumping operation and have a reciprocating plunger disposed therein. The outwardly directed forces applied to such protuberance in the course of plunger reciprocation would lead to ultimate, if not immediate, destruction of the pipe.

An outer longitudinal strand assemblage 71 in the vicinity of resin threads 54 is desired (see FIG. 3) to afford added shear strength to the threads. Interposed assemblages 53 and 55 also afford shear strength. The longitudinally tensioned strands spaced outwardly from the resin threads tend to dissipate shear stresses which otherwise might deleteriously affect the threads. The outermost glass roving application employed in the course of formation of the pipe pin end is also a longitudinal assemblage to facilitate slidable movement thereover of a male-thread mold 60, more clearly seen in section in FIGURE 4. It will also be noted from FIG. 4 that the final roving layer between the upsets 56 and 56p is preferably -a spiral layer 33 of overlapping strand helices which serves as a locking layer retaining all underlying strands in place.

Mold 60 is employed in conjunction with opposed plastic caps 62 and 64. It is the function of the mold 6t) and associated caps 62 and 64'to assist in the formation of male threads about the pin portion of the pipe oppositely disposed to the coupling end portion.

In the normal course of use of the mold 60, a res-in parting agent 63 is applied over the threaded surface 66. A thickened resin composition 70, such as that previously described, which will ultimately form the male threads of the final pipe product, is applied to the threaded surface 66. For a two and one-half inch pipe the diameter of opening 62a in the cap 62 is approximately onesixteenth inch larger than larger mold passageway opening I immediately therebeneath and is spaced about one-eighth inch from the underlying mold. It is seen from FIG. 6 that surface 66 defines a threaded, tapered pas sageway. Cap 64 disposed in part about the smaller opening s of the mold 60 has an opening 64a disposed therein which is approximately one-fourth inch smaller than the diameter of tubing about which the male threads are to be formed.

Following application of the thickened resin mixture to the threaded surface 66 of the mold 60, the die and cap assembly, together with the resin, is pushed over the pin end of the tubing so as to obtain a position such as is illustrated in FIG. 4. It will be noted from FIG. 4 that the outermost roving layer adjacent the threads formed from the resinous composition 70 is composed of longitudinal strands 71 to both facilitate slidable movement thereover of the mold and also afford shear strength to the threads formed thereover. In the course of obtaining the position of FIG. 4, the resin disposed about the outer periphery of the formed, but uncured, pipe has not yet set and securely bonds with the thickened, but plastic, resin mixture applied to the mold surface 66. Consequently, as the mold and tube assembly is moved to the left, as illustrated in FIG. 4, cap portion 65 defining an opening of lesser diameter than the outer diameter of the pipe pin end portion is coned outwardly away from the opposed cap 62.

Portion 65 of cap64 functions as a wiper forcing the resin on the pipe and initially coated on the mold into the mold threaded portions thereby displacing any air between the mold and the pipe, in which interval the resin threads are formed. Portion 67 of cap 62 allows excess resin to emerge from between the mold and pipe during mold movement and in the final position may assist in centering the mold by engaging built-up pipe portion 56a. Portion 67 also functions as a reservoir from which resin may be fed back between the mold and pipe should any voids be disposed therein.

The cap portion disposed about the larger opening I of the mold threaded passageway may have inwardly projecting centering fingers f, as indicated in modified cap 62m illustrated in FIG. 7. The fingers 1 may lie on a periphery of precisely the same diameter as the pipe end portion encompassed thereby. Thus, the fingers 1 will not flex in the direction of the threads being formed and interfere with proper thread formation in the course of centering the mold relative to the surrounded pipe end. The number of fingers 1 need only be sufficient to center the cap 62m and provide plenty of space therebetween through which excess resin may escape if necessary. A desired reservoir is still available utilizing the cap of FIG. 7.

Following application of the mold and cap construction of FIG. 5, the resulting assembly, including the mandrel, the pipe formed thereon, the coupling end mold and the pin end mold, is rotatably mounted on a curing table. The pipe is rotated to insure uniformity ofresin disposition about the pipe periphery and subjected to a curing temperature during the course of which the resin component of the formed pipe is cured and the glass filaments further stressed by mandrel expansion. Following curing of the pipe, the prestressing ring 20 may be separated from the mandrel and pipe assembly by cutting the pipe approximately in the plane of the mandrel shoulder 24 In "order to minimize wastage and facilitate final pipeapparatus separation, the spiral windings should not be formed any. significant distance past the terminal thread of nipple 14 disposed adjacent the nipple unthreaded portion. Following removal of the ring 20 from the mandrel, the thin pipe portion covering the screw 16 is peeled back, allowing the fastener to be loosened. The nipple is then unscrewed from the pipe.

It is seen, therefore, from the foregoing that a novel method and apparatus has been disclosed for the formation of a glass-reinforced resin pipe having coupling and pin ends, dispensing with the need for any discrete coupling member.

The provided methods and apparatus for forming threads assure maximum thread strength and require a minimum of processing time. The various threads and molds therefor illustrated embody a taper corresponding to tapers normally found in threaded devices.

Without further elaboration, the foregoing will so fully explain the character of my invention that others may, by applying current knowledge, readily adapt the same for use under varying conditions of service, while retaining certain features which may properly be said to constitute the essential items of novelty involved, which items are intended to be defined and secured to me by the following claims.

I claim:

1. A glass-reinforced resin pipe consisting essentially of cured resin and tensioned strands of longitudinal and helical glass filaments arranged substantially parallel and transversely, respectively, to the longitudinal axis of said pipe and embedded in said cured resin; said pipe having a fiber-reinforced resin thread bonded to longitudinal glass filaments of said pipe under tension.

2. The glass-reinforced resin pipe of claim 1 in which the resin thereof is epoxy resin.

3. The glass-reinforced resin pipe of claim 1 in which said glass filaments are untwisted.

4. A glass-reinforced resin pipe consisting essentially of cured resin and tensioned strands of longitudinal and helical glass filaments arranged substantially parallel and transversely, respectively, to the longitudinal axis of said pipe embedded in said cured resin; said pipe having an internally threaded coupling end and an opposed externally threaded end; the threads of said pipe ends comprising cured resin threads reinforced against shear forces by longitudinal glass filaments of said pipe under tension 0 to which bonded.

5. The glass-reinforced pipe of claim 4 in which said glass filaments are untwisted.

6. A glass-reinforcedresin pipe consisting essentially of cured resin and tensioned strands of longitudinal and spiral glass filaments arranged substantially parallel and transversely, respectively, to the longitudinal axis of said pipe embedded in said cured resin; said pipe having an internally threaded end, the internal threads of said end comprising cured resin having glass filament spirals embedded in the crest portions thereof; said internal threads being bonded to longitudinal glass filaments of said pipe under tension.

References Cited UNITED STATES PATENTS 885,219 4/1908 Bayne et al 138-130 2,723,705 11/1955 Collins 138144 X 2,751,237 6/1956 Conley 285-423 2,943,967 7/1960 Simon 285-423 X 3,098,664- 7/1963 Waugh 138109 X 3,200,023 8/1965 Cilker 138l44 X LAVERNE D. GEIGER, Primary Examiner.

C. L. HOUCK, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 ,381,716 May 7, 1968 Vesta F. Michael It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2, line 5, "abject" should read object Column 3, line 32, "3,202,650" should read 3,202,560 line 40, after "45,000" insert pounds Signed and sealed this 16th day of September 1969.

(SEAL) Attest:

Edward M. Fletcher, J1

Attesting Officer Commissioner of Patents WILLIAM E. SCHUYLER, JR. 

